The proposed research involves a study of lens regeneration from the iris and neural retina regeneration from the pigmented, retinal epithelium. It is hoped to obtain information concerning the stimuli which release the processes of metaplasia taking place and the role of trophic factors during the course of regeneration. Synthesis of macromolecules and cytological changes in the reacting tissues will also be studied. Some of the aspects to be investigated are the ultrastructural and synthetic events taking place in lens capsule formation and ultrastructural changes during dedifferentiation of the iris and beginning lens differentiation during lens regeneration in young and old larvae and in adult newts. The role of the vitreous body in transmitting the neural retinal trophic factor to the iris, possible mechanisms for the inhibitory action of lens on lens regeneration, the effect of a carcinogen and of growth factors on lens regeneration and possible similarities between the actions of the lens inductor from the embryonic eyecup and the neural retinal trophic factor in lens regeneration will be studied. In addition, releasing mechanisms for neural retina regeneration and the pattern of uptake of tritiated uridine and amino acids during this process will be investigated.